Facebook weighed charging other apps for access to its developer tools, including the friends lists, if they did not buy a certain amount of advertising from Facebook, according to the emails.

Facebook gave certain companies like Lyft, Netflix and Airbnb preferential treatment by allowing them to access users' data, according to a massive trove of secret documents and emails released by a British parliamentary committee on Wednesday.

The UK parliament's select media committee published more than 200 pages of internal Facebook emails it has acquired while probing how the giant was being used to manipulate major election results The UK parliament's select media committee published more than 200 pages of internal Facebook emails it has acquired while probing how the giant was being used to manipulate major election results.

In one email, dated January 23 2013, a Facebook engineer contacted Zuckerberg to say that rival Twitter Inc. had launched its Vine video-sharing tool, which users could connect to Facebook to find their friends there. Alerted to the possible competitive threat by an engineer who recommended cutting off Vine's access to Facebook data, Zuckerberg replied succinctly: "Yup, go for it". He also said that a change to Facebook's Android app policy that resulted in call and message data being recorded was deliberately made hard for users to know about.

"We stand by the platform changes we made in 2015 to stop a person from sharing their friends' data with developers", the company said in a statement.

Facebook also used Onavo (an Israeli analytics company it bought in 2013) to observe users' overall usage of its mobile apps without their approval or knowledge in order to figure out how many users had downloaded apps and how often they used them.

Facebook, which has described the Six4Three case as baseless, said the released communications were "selectively leaked" and it defended its practices. He'd obtained the documents after compelling the founder of US software company Six4Three to hand them over during a business trip to London.

The documents were part of a California lawsuit filed by app developer Six4Three. The idea of tying access to this data to the developer's relationship with Facebook is a recurring feature throughout the documents. "Like any business, we had many of internal conversations about the various ways we could build a sustainable business model for our platform". This year, he had to testify in front of U.S. Congress on one such instance of a developer sharing user data with Cambridge Analytica, the political consultancy.

The internal emails also detail discussions regarding the collection of call and text logs from Android users.